Low power read operation for programmable resistive memories

ABSTRACT

A programmable resistive memory has a plurality of programmable resistive devices (PRD) and at least one sensing circuit. The at least one of the programmable resistive device can include at least one programmable resistive element (PRE). The sensing circuit can include one PRD unit and a reference unit. Each unit has at least one capacitor to charge to a second supply voltage line and to discharge to the first supply voltage line through the PRE and the reference element, respectively. The capacitors are also coupled to comparators to monitor discharging voltages with respect to a reference voltage. By comparing the time difference when the comparators change their outputs, the magnitude of the PRE resistance with respect to the reference element resistance can be determined and converted into logic states.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority benefit of U.S. Provisional Patent Application No. 62/485,895, filed on Apr. 14, 2017 and entitled “CIRCUIT AND SYSTEM OF ULTRA LOW VOLTAGE AND LOW CURRENT READ FOR PROGRAMMABLE RESISTIVE MEMORIES,” which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a sensing circuit for converting resistance in programmable resistive devices into logic states. The programmable resistive device memories are OTP, MTP, PCRAM, FeRAM, RRAM, and MRAM, etc.

Description of the Related Art

A Programmable Resistive Device (PRD) is generally referred to a device whose resistance can be changed by means of programming. Resistance states can also be determined by resistance values. For example, a programmable resistive device can be a One-Time Programmable (OTP) device, such as electrical fuse (or anti-fuse), and the programming means can apply a high voltage to induce a high current to flow through the OTP element. When a high current flows through an OTP element (e.g., by turning on a selector), the OTP element can be programmed, or burned into a high or low resistance state (depending on either fuse or anti-fuse).

FIG. 1 shows a schematic diagram of a conventional Programmable Resistive Device (PRD) 10 that has a Programmable Resistive Element (PRE) 11 and a selector 12. The PRE 11 can be an electrical fuse, anti-fuse, floating-gate device, phase-change material, resistive RAM element, or Magnetic Tunnel Junction (MTJ), etc. The selector 12 can be MOS, diode, MOS/diode merged, or even bipolar device that can be turned on or turned off by asserting a signal Sel.

The resistance of a PRE in a PRD device needs to be converted into a logic level after reading the PRD cell. This can be achieved by using a sensing circuit or sense amplifier (SA). The conventional way of sensing a PRE resistance is to convert the resistance value into a voltage by applying a current flowing through the PRE, then using a voltage amplifier to enlarge the voltage signal. This scheme depends on amplification of a MOS device that usually needs to be biased with substantial amount of current to have high gain.

FIG. 2 is a schematic diagram of a conventional sense amplifier 20. The SA 20 has a PMOS 21 with the gate coupled to the drain. The gate of PMOS 21 is also coupled to a gate of PMOS 22. The sources of PMOS 21 and 22 are coupled to a supply voltage VDD. The drains of PMOS 21 and 22 are coupled to drains of NMOS 23 and 24, respectively. The gates of NMOS 23 and 24 are coupled to a differential input signal, Vp and Vn, respectively. The sources of NMOS 23 and 24 are coupled to a drain of a NMOS 26, whose gate is coupled to an enable signal ϕ and whose source is coupled to ground. The input differential voltage between Vp and Vn can be amplified to the output Vout, at the drain of PMOS 22.

FIG. 3 is a schematic diagram of another conventional voltage sense amplifier 30. The scheme is to bias MOS devices in a latch into high gain region to amplify the differential signals and then latching the signals into two stable logic states. Biasing MOS in high gain region normally requires substantial amount of current. A PMOS 31 has a source coupled to a supply voltage VDD, a drain coupled to a drain of an NMOS 33, whose source is coupled to a drain of another NMOS 35. The gate of NMOS 33 is coupled to an input voltage V+. The gate of NMOS 35 is coupled to the gate of PMOS 31. There is also another similar branch that has a PMOS 32 having a source coupled to a supply voltage VDD, a drain coupled to a drain of a NMOS 34, whose source is coupled to a drain of another NMOS 36. The gate of NMOS 34 is coupled to another input voltage V−. The gate of NMOS 36 is coupled to the gate of PMOS 32. The sources of the NMOS 35 and 36 are coupled to a drain of an NMOS 39, whose gate is coupled to an enable signal ϕ and whose source is coupled to ground. The input differential signals of V+ and V− can be amplified to Vn and Vp, respectively, by turning on the enable signal ϕ. There are also another embodiments of voltage sensing by placing NMOS 33 and 34 between PMOS 31 and 32 and the supply voltage or placing them between NMOS 35 and 36 and the drain of the tailing NMOS 39.

The conventional approaches to voltage sensing in FIG. 2 or FIG. 3 depending on the supply voltage VDD and MOS threshold voltages Vtn and Vtp to bias the MOS devices in high gain region, which normally needs some amount of current. If the supply voltage is 0.8V and the Vtn and |Vtp| are about 0.3V, sensing the PRD with only 0.4V would be very difficult for MOS to be in high gain regions. Even if the voltage sense amplifier was able to operate, the MOS bias current in high gain region would be substantial for an sense amplifier (SA) to work. At least 100 uA would be needed to do so and achieving 1 uA of sensing current would be almost impossible. In IoT applications, there are some requests for sensing programmable resistive devices with only 0.4V voltage and 1 uA current, while the nominal supply voltage is 0.8V.

The conventional approaches to sensing a resistance by converting into voltage requires high supply voltage and high current. However, the industry trend in semiconductors is use of low supply voltage and low current consumption, especially in PC, tablet, smart phone, portable, and IoT applications. Thus, there is a need for improved approaches to sense resistance of programmable resistive memory cells under low voltage and low current conditions.

SUMMARY OF THE INVENTION

Embodiments of sensing programmable resistive device cells in low supply voltage with low current are disclosed. The methods and circuits of low voltage and low current sensing can be used in any kind of programmable resistive memories, such as OTP, MTP, PCRAM, RRAM, FeRAM, and MRAM, etc.

In one embodiment, a capacitor can be charged to near a supply voltage during a first period of time. Then, the capacitor can be discharged through a resistance in a second period of time. A voltage at the discharging capacitor can be compared with a reference voltage to change a memory read output. The time for an output logic device (e.g., comparison device) to change its output is determined by a product of the resistance and capacitance of the comparator. Since the capacitance is known, the time for the output logic device to change the output is related to the resistance value. Thus, the resistance can be determined by the time delay since start of the discharging. The longer the time delay, the larger the resistance. In this circuitry. In one implementation, MOS devices are only used as switches to turn on or off for charging or discharging. Therefore, the threshold voltages of the MOS devices are not crucial in this time-based sensing scheme.

The invention can be implemented in numerous ways, including as a method, system, device, or apparatus (including graphical user interface and computer readable medium). Several embodiments of the invention are discussed below.

As a programmable resistive memory, one embodiment can, for example, include at least a plurality of programmable resistive device (PRD) cells, and a time-based sensing circuit. The time-based sensing circuit can include at least: a capacitor selectably connected to a voltage source line; a selector controlled by a control signal, the selector having a first end and a second end, the second end being coupled to a first conductive line; a programmable resistive element (PRE) having a first end coupled to the capacitor and a second end coupled to the first end of the selector; and a comparator coupled to the first end of the PRE. The time-based sensing circuit can use different discharge times to determine resistance of the PRE.

As an electronic system, one embodiment can, for example, include at least a processor, and a programmable resistive memory operatively connected to the processor. The programmable resistive memory can include at least a plurality of programmable resistive device (PRD) cells for providing data storage, each of the PRD cells can include at least: a capacitor selectably connected to a voltage source line; a selector controlled by a control signal, the selector having a first end and a second end, the second end being coupled to a first conductive line; a programmable resistive element (PRE) having a first end coupled to the capacitor and a second end coupled to the first end of the selector; and a logic device coupled to the first end of the PRE.

As an electronic system, one embodiment can, for example, include at least a processor, and a programmable resistive memory operatively connected to the processor. The programmable resistive memory can include at least a plurality of programmable resistive device (PRD) cells for providing data storage. Each of the programmable resistive device cells can include at least a programmable resistive element (PRE) coupled to a first supply voltage line through a selector with an enable signal, and a time-base sensing circuit coupled to at least one PRD cell unit and a reference unit having the PRE and reference resistor, respectively; each unit has at least one capacitor that can be charged to a second supply voltage line and discharged through PRE and reference resistor, respectively, to the first supply voltage line; each unit has at least one comparator coupled to the capacitor to change output when the voltage discharged to a reference voltage. The PRE resistance can be converted into logic state by the time difference of the comparators changing outputs.

As a method for providing a programmable resistive memory including a plurality of programmable resistive device cells, at least one of the programmable resistive device cells including at least a programmable resistive element and a capacitor, one embodiment can, for example, include at least: charging the capacitor; ceasing the charging; subsequently coupling the programmable resistive element to the capacitor; monitoring a discharge rate of the capacitor while the programmable resistance element remains coupled to the capacitor; determining a resistance value of the programmable resistive element based on the monitoring of the discharge rate; and determining a logic state for the at least one of the programmable resistive device cells based in the determined resistance value of the programmable resistive element.

As a method for providing a programmable resistive memory, one embodiment can, for example, include at least providing a plurality of programmable resistive device cells, at least one of the programmable resistive device cells include at least (i) a programmable resistive element coupled to a first supply voltage line through a selector with an enable signal; and (ii) a time-base sensing circuit coupled to at least one PRD cell unit and a reference unit having PRE and a reference resistor, respectively; each unit has at least one capacitor that can be charged via a second supply voltage line and discharged through PRE and reference resistor, respectively, via the first supply voltage line; each unit has at least one comparator coupled to the respective capacitors to change output when the voltage discharged is compared to a reference voltage. The method can further include turning on the enable signal of the PRD unit and reference unit, after the capacitors are charged to the second supply voltage approximately, to discharge the capacitors through the PRE and reference element respectively; and converting the PRE resistance into logic states by the time difference of the comparator output changes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the following detailed descriptions in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which:

FIG. 1 shows a schematic diagram of a conventional programmable resistive memory device.

FIG. 2 shows a schematic diagram of a conventional voltage sense amplifier.

FIG. 3 shows a schematic diagram of a another conventional voltage sense amplifier.

FIG. 4(a) illustrates a schematic diagram of a low power sensing circuit according to one embodiment.

FIG. 4(b) illustrates a timing waveform of a voltage being discharged according to one embodiment.

FIG. 5(a) illustrates a schematic diagram of time-based sensing circuit according to one embodiment.

FIG. 5(b) illustrated a timing waveform of discharging capacitor voltages in a cell unit and a reference unit, according to one embodiment.

FIG. 6 is a flow diagram of a method of converting resistance into time according to one embodiment.

FIG. 7 is a flow diagram of a method of time-based resistance sensing according to one embodiment.

FIG. 8 shows a processor system with at least one programmable resistive memory using low voltage and low current sensing circuit, according to one embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments disclosed herein use capacitors discharging through programmable resistance element (PRE) to evaluate a programming state. By comparing a discharging time to reach a predetermined voltage, the PRE can be converted into a logic state. The discharging time can be compared with a discharge time provided by a separate unit that used a reference resistance. For example, comparison of discharging time to reach a predetermined voltage in two different units enables the resistance of the PRE to be evaluated and converted into a logic state.

In one embodiment, a programmable resistive memory has a plurality of programmable resistive devices (PRD) and at least one sensing circuit. The at least one of the programmable resistive device can include at least one programmable resistive element (PRE). The sensing circuit can include one PRD unit and a reference unit. Each unit has at least one capacitor to charge to a second supply voltage line and to discharge to the first supply voltage line through the PRE and the reference element, respectively. The capacitors are also coupled to comparators to monitor discharging voltages with respect to a reference voltage. By comparing the time difference when the comparators change their outputs, the magnitude of the PRE resistance with respect to the reference element resistance can be determined and converted into logic states.

The programmable resistive element and a sensing circuit can be included in a Programmable Resistive Device (PRD). Optionally, the programmable resistive element and a sensing circuit can be included within an electronic system.

The PRD can be a One-Time Programmable (OTP) device, such as electrical fuse (or anti-fuse). A current that flows through an OTP element (e.g., by turning on a selector) can program the OTP element or can burned the OTP element into a high or low resistance state (depending on either fuse or anti-fuse). The electrical fuse can be an interconnect or contact/via fuse. The interconnect fuse can be made of MOS gate, polysilicon, silicide, silicided polysilicon, metal, metal alloy, or thermally isolated active region. The contact or via fuse can be made of a single or a plurality of contact or via holes for programming. The anti-fuse can be made of breaking down a MOS oxide or a dielectric between conductors. The PRD can also be other kinds of memory devices, such as MTP, PCRAM, RRAM, Fe RAM, and MRAM that can be programmed more than once.

Any MOS devices in this sensing circuit are used as switches. Therefore, their threshold voltages related to the supply voltage are not crucial to the operation of the circuit. Thus, low voltage and low current sensing can be achieved in standard CMOS logic process without additional masks or process steps to save costs.

FIG. 4(a) illustrates a schematic diagram of a low power sensing circuit 50 according to one embodiment. The sensing circuit 50 has a switch 52 coupled to a supply voltage VDD and to ground through a capacitor 51. The capacitor 51 is coupled to a switch 54 then to a resistive device 53 to ground. The capacitor 51 can be charged to VDD by turning on the switch 52 and turning off the switch 54. After the capacitor 51 is fully charged, the capacitor 51 can be discharged by turning on the switch 54 and turning off the switch 52. Thus, the voltage at node A at the capacitor 51 can be discharged according to a RC-time constant. The RC-time constant is dependent on the product of R and C. Since the capacitance (C) of the capacitor 51 can be fixed, the discharge rate will depend on resistance (R) of the resistive device 53.

FIG. 4(b) illustrates a timing waveform of a voltage at node B being discharged according to one embodiment. If the resistance of the resistive device 53 has a larger resistance than a reference resistance, the discharge curve would look like 62. Conversely, if the resistance of the resistive device 53 has a smaller resistance than the reference resistance, the discharge curve would look like 61. If one-half VDD (Vdd/2) is the predetermined voltage, time delays is and tl for curves 61 and 62, respectively, to reach the predetermined voltage are as shown in FIG. 4(b). The larger the resistance, the longer the time delay. In other words, the sensing circuit 50 converts resistance into time, as is depicted in FIG. 4(b) which relates voltage to time.

FIG. 5(a) illustrates a schematic diagram of time-based sensing circuit 100, according to one embodiment. The time-based sensing circuit 100 has a cell unit 120 and a reference unit 130. The cell unit 120 has a capacitor 101 coupled to a supply voltage VDD through a charging pass gate 102 and coupled to a ground. The capacitor 101 is also coupled to a discharge pass gate 106. The discharge pass gate 106 couples to a programmable resistive device 103. The programmable resistive device 103 includes a programmable resistive element 104 coupled in series with a selector 105 that couples to ground. The discharge pass gate 106 is also coupled to an inverter 107, which can serve as a comparator or logic state converter.

The reference unit 130 has a capacitor 111 coupled to a supply voltage VDD through a charging pass gate 112 and coupled to a ground. The capacitor 111 is also coupled to a discharge pass gate 116. The discharge pass gate 106 couples to a reference device 113. The reference device 113 includes a reference element 114 coupled in series with a selector 115 that couples to ground. The discharge pass gate 116 is also coupled to an inverter 117, which can serve as a comparator or a logic state converter. The output of the inverters 107 and 117 can be coupled to an input and an enable a flip-flop 108, respectively. The output QB of the flip-flop 108 can represent a logic state of the PRE 104 with respect to the reference element 114.

The operation of time-based sensing circuit can be further elaborated as follows. The cell unit 120 includes the capacitor 101 and the reference unit 130 includes the capacitor 111. The capacitors 101 and 111 typically have the same capacitance C. The capacitors 101 and 111 can be charged to near VDD with assertion of CKB which turns on the charge pass gates 102 and 112, while the discharge pass gates 106 and 116 are turned off. When the capacitors 101 and 111 are nearly full charged, the charge pass gates 102 and 112 are turned off and the discharge pass gates 106 and 116 as well as the selectors 105 and 115 are turned on. The capacitors 101 and 111 will then be respectively discharged through the resistance of the PRE 104 and the reference element 114. The capacitors 101 and 111 are also coupled to inverters 107 and 117, respectively, that serve as logic comparators to generate logic states. Before discharge, the outputs of the inverters 107 and 117, as comparators, are all 0s. When the capacitor voltages have discharged below trip points of the inverters 107 and 117, the outputs of the inverters 107 and 117 will be independently changed to 1 s. If the output of the inverter 117 is changed to 1, the flip-flop 108 will be turned on to latch the output of the inverter 107. The output QB will be high if the resistance of the PRE 104 in the cell unit 120 has lower resistance than the resistance of reference element 114; otherwise, the flip-flop output QB will be low.

FIG. 5(b) illustrates a timing waveform 200 of the capacitor voltages at nodes Bc and Br in the cell unit 102 and the reference unit 130, respectively, according to one embodiment. A curve 202 shows discharging of the capacitor 111 in the reference unit 130. When the voltage at node Br reaches half VDD (Vdd/2), which is set as the trip point of the inverter 117, the output of the inverter 117 will become high. Then, the flip-flop will latch data 1 or 0 for curves 201 or 203, respectively, depending on whether the resistance of the PRE 104 in the cell unit 120 is lower or higher than the resistance of the reference element 114.

The time-based sensing circuit in FIG. 5(a) is merely an exemplary embodiment, many alterations or variations are possible. The pass gates can be embodied as NMOS, PMOS, or full CMOS pass gates. The capacitors can be made of MOS gate capacitor, Poly-Isolator-Poy (PIP), Metal-insulator-Metal (MIM) capacitor, or other type of capacitors. If MOS gate capacitor is used, thick oxide I/O devices are preferred over the core logic devices to reduce leakage current. The comparison devices (e.g., inverters or flip-flop) can be embodied as any kind of analog comparators or sense amplifiers, either static or dynamic comparators. The comparison devices can also be an arrangement of logic gates, such as inverters or Schmitt triggers to switch output when the input reaches certain voltage level. The reference voltage used for comparison can be any voltage between VDD and ground, though half VDD (Vdd/2) is a convenient voltage. The pass gates 106 and 116 can be omitted in some embodiments. The time to charge capacitors can be made longer than discharging time to reduce peak current in some embodiments, i.e. charging or discharging duty cycle need not be 50%. A transparent latch or flip-flop can be used to latch the output data in some embodiments. There can be many different varieties and yet equivalent embodiments and they all fall into the scope of this invention.

FIG. 6 is a flow diagram of a method 300 of converting resistance into time according to one embodiment. In the first step 310, a capacitor having a capacitance C is charged to near a supply voltage such as VDD. In the second step 320, the capacitor is discharged through a resistive device having a resistance R. In the third step 325, a fixed voltage is acquired as a reference voltage level. The fixed voltage can be previously determined or determined when needed. In the fourth step 330, compare the discharging voltage with the reference voltage level to determine if the discharging voltage has reached the reference voltage level. In the fifth step 340, the time from starting discharging the capacitance C of the capacitor until discharging voltage is determined to be at or less than the reference voltage level is determined by R*C. Since the capacitance C is fixed, the resistance R can be determined accordingly.

FIG. 7 is a flow diagram of a method 400 of time-based resistance sensing according to one embodiment. The method 400 can use a PRD cell and a reference unit. In the step 410, at least two capacitors are charged to near a supply voltage VDD. One capacitor is part of the PRD cell, and another capacitor is part of the reference unit. In the step 420, the two capacitors are discharged through a Programmable Resistive Element (PRE) and a reference element, respectively. The PRD cell includes the PRE, and the reference unit includes the reference element. In one implementation, the discharging can be initiated by turning on selectors. In the step 425, a fixed reference voltage to check voltage discharging can be determined. In the step 430, the fixed reference voltage can be compared with discharged voltages using comparators. The comparator outputs can independently change when the discharge voltages are discharged below the reference voltage level. In the step 440, the comparator output of the reference unit can be turned on to trigger a flip-flop when the discharge voltage level in the reference unit is discharged below the reference voltage level. In the step 450, the comparator output of the PRD cell is used as an input to the flip-flop. In the step 460, the output of the flip-flop is a logic state for the PRE resistance.

FIG. 8 shows a processor system 700 according to one embodiment. The processor system 700 can include a programmable resistive device 744 and a time-base sensing circuit 742, in a programmable resistive memory 740, according to one embodiment. The processor system 700 can, for example, pertain to a computer system. The computer system can include a Central Process Unit (CPU) 710, which communicate through a common bus 715 to various memory and peripheral devices such as I/O 720, hard disk drive 730, CDROM 750, programmable resistive memory 740, and other memory 760. Other memory 760 is a conventional memory such as SRAM, DRAM, or flash, typically interfaces to CPU 710 through a memory controller. CPU 710 generally is a microprocessor, a digital signal processor, or other programmable digital logic devices. Programmable resistive memory 740 is preferably constructed as an integrated circuit, which includes a plurality of programmable resistive devices 744 in a memory array and at least one time-base sensing circuit 742. The programmable resistive memory 740 typically interfaces to CPU 710 with simple interface control or through a memory controller. If desired, the programmable resistive memory 740 may be combined with the processor, for example CPU 710, in a single integrated circuit.

The invention can be implemented in a part or all of an integrated circuit in a Printed Circuit Board (PCB), or in a system (electronic system, computing system, etc.). The programmable resistive memory can be fuse, anti-fuse, or emerging nonvolatile memory. The fuse can be silicided or non-silicided polysilicon fuse, metal fuse, thermally-isolated-active-area fuse, contact fuse, via fuse, or trench silicide in FinFET, or FinFET itself. The anti-fuse can be a gate-oxide breakdown anti-fuse, contact or via anti-fuse with dielectrics in-between. The emerging nonvolatile memory can be Magnetic RAM (MRAM), Phase Change Memory (PCM), Conductive Bridge RAM (CBRAM), Ferroelectric RAM (FeRAM) or Resistive RAM (RRAM). Though the program mechanisms are different, their logic states can be distinguished by different resistance values.

The above description and drawings are only to be considered illustrative of exemplary embodiments, which achieve the features and advantages of the present invention. Modifications and substitutions of specific process conditions and structures can be made without departing from the spirit and scope of the present invention.

The many features and advantages of the present invention are apparent from the written description and, thus, it is intended by the appended claims to cover all such features and advantages of the invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation as illustrated and described. Hence, all suitable modifications and equivalents may be resorted to as falling within the scope of the invention. 

What is claimed is:
 1. A programmable resistive memory, comprises: a primary cell including at least: a selector controlled by a control signal, the selector having a first end and a second end, the second end being coupled to a first conductive line; a capacitor selectively coupled to a second conductive line; and a programmable resistive element (PRE) having a first end able to be coupled to the capacitor and a second end coupled to the first end of the selector; and a reference cell including at least: a reference selector controlled by the control signal, the reference selector having a first end and a second end, the second end being coupled to the first conductive line; a reference capacitor selectively coupled to the second conductive line; and a reference resistance element having a first end able to be coupled to the reference capacitor and a second end coupled to the first end of the reference selector, wherein a discharge time of the PRE relative to a discharge time of the reference resistance element is used to determine resistance of the PRE.
 2. A programmable resistive memory as recited in claim 1, wherein the programmable resistive memory comprises: a primary logic device able to be coupled to the first end of the PRE and operable to provide a primary logic state of the primary cell, and a reference logic device able to be coupled to the first end of the reference resistance element and operable to provide a reference logic state of the reference cell.
 3. A programmable resistive memory as recited in claim 2, wherein the programmable resistive memory includes at least one reference cell and a plurality of programmable resistive device (PRD) cells, each of the PRD cells including the primary cell, and wherein the programmable resistive memory comprises: an output logic device to output a logic state of the at least one of the PRD cells, the output logic device being coupled to the primary logic device and the reference logic device.
 4. A programmable resistive memory as recited in claim 1, wherein the programmable resistive element comprises one-time programmable (OTP) element in OTP memory, magnetic tunnel junction (MTJ) in an MRAM or RRAM element in an RRAM.
 5. A programmable resistive memory, comprises: a plurality of programmable resistive device (PRD) cells; and a time-based sensing circuit including at least: a selector controlled by a control signal, the selector having a first end and a second end, the second end being coupled to a first conductive line; a capacitor selectively coupled to a second conductive line; a programmable resistive element (PRE) having a first end coupled to the capacitor and a second end coupled to the first end of the selector; and a comparator coupled to the first end of the PRE, wherein the time-based sensing circuit using different discharge time to determine resistance of the PRE, wherein the programmable resistive element is an one-time programmable (OTP) element that comprises at least one of an anti-fuse, fuse or floating-gate device.
 6. A programmable resistive memory, comprises: a plurality of programmable resistive device (PRD) cells; and a time-based sensing circuit including at least: a selector controlled by a control signal, the selector having a first end and a second end, the second end being coupled to a first conductive line; a capacitor selectively coupled to a second conductive line; a programmable resistive element (PRE) having a first end coupled to the capacitor and a second end coupled to the first end of the selector; and a comparator coupled to the first end of the PRE, wherein the time-based sensing circuit using different discharge times to determine resistance of the PRE, wherein the programmable resistive element comprises at least one of RRAM or MRAM device.
 7. A programmable resistive memory as recited in claim 1, wherein the programmable resistive memory comprises: a primary switch coupled to the first end of the PRE, and a reference switch coupled to the first end of the reference resistance element.
 8. An electronic system, comprises: a processor; and a programmable resistive memory operatively connected to the processor, the programmable resistive memory includes at least a plurality of programmable resistive device (PRD) cells for providing data storage, each of the programmable resistive device cells comprising: a programmable resistive element (PRE) coupled to a first supply voltage line through a selector with an enable signal; and a time-base sensing circuit coupled to at least one PRD cell unit and a reference unit having a PRE and a reference resistor, respectively; each of the PRD cell unit and the reference unit are coupled to capacitors that can be charged to a second supply voltage line and discharged through the PRE and the reference resistor, respectively, to the first supply voltage line; the PRD cell unit and the reference unit are coupled to at least one comparator to change output logic state when the voltages are discharged to a reference voltage, wherein the capacitors in both units are charged to the second supply voltage approximately and discharged to the first supply voltage line by turning on the enable signal at the same time, and wherein the PRE resistance can be converted into logic state based on different discharge rates by the PRD cell unit and the reference unit.
 9. An electronic system as recited in claim 8, wherein the comparator outputs of the cell and reference units are coupled to latches or flip-flops, respectively, and an output of the latch or flip-flop depends on whether the PRE resistance is larger or smaller than the reference resistance.
 10. An electronic system as recited in claim 8, wherein the reference voltage for the comparator is approximately half way between the first and the second supply voltages.
 11. An electronic system as recited in claim 8, wherein the programmable resistive element comprises at least one of floating-gate device, electrical-fuse, phase-change film in PCRAM, resistive film in RRAM, ferroelectric film in FeRAM, or magnetic tunnel junction in MRAM.
 12. An electronic system as recited in claim 8, wherein the programmable resistive element comprises at least one of polysilicon, silicided polysilicon, silicide, metal, metal alloy, thermal isolated active region, trench silicide in FinFET, FinFET itself, or MOS gate.
 13. An electronic system as recited in claim 8, wherein the programmable resistive element is an anti-fuse fabricated by a single or plural of contacts or vias with dielectrics in between, or an anti-fuse comprising of a CMOS gate and a CMOS body with gate oxide in between.
 14. An electronic system as recited in claim 8, wherein the comparator is an inverter.
 15. A method for providing a programmable resistive memory, comprising: providing a plurality of programmable resistive device cells, at least one of the programmable resistive device cells include at least (i) a programmable resistive element coupled to a first supply voltage line through a selector with an enable signal; and (ii) a time-base sensing circuit coupled to at least one PRD cell unit and a reference unit having a PRE and a reference resistor, respectively; the PRD cell unit and the reference unit are coupled to at least one capacitor that can be charged to a second supply voltage line and discharged through the PRE and the reference resistor, respectively, to the first supply voltage line; the PRD cell and the reference unit are coupled to at least one comparator, and wherein the comparator changes output logic states based on a comparison of the voltage discharged to a reference voltage; turning on the enable signal of the PRD unit and reference unit, after the capacitors are charged to the second supply voltage approximately, to discharge the capacitors through the PRE and reference element respectively; and converting the PRE resistance into logic states by the time difference of the comparator output changes.
 16. A method as recited in claim 15, wherein the programmable resistive device cells are one-time programmable memory cells.
 17. A method as recited in claim 16, wherein a discharge rate is dependent on capacitance of the capacitor and the resistance value.
 18. A method as recited in claim 17, wherein the programmable resistive element comprises at least one MRAM device.
 19. A method as recited in claim 17, wherein the programmable resistive element comprises at least one RRAM. 